The present invention is generally related to the use of ultrasonic energy for the ablation of atheroma and dissolution of blood clots in vessels and is more particularly directed to the intravascular generation of ultrasonic energy for removal of intravascular blockages by ablation thereof.
The accumulation of atheromas (atherosclerosis) or the formation of thrombi in a blood vessel may seriously impair circulation and if blockage occurs, distal tissues may be deprived of oxygen and nutrients, thereby resulting in disruption of cell tissue.
The thickening of atheroma reduces the elasticity of the blood vessel and significantly restricts the free passage of blood through a vessel, resulting in a stenosis such that even a small thrombus may become lodged, creating an infarct or occlusion.
A number of alternative methods and apparatus have been used in the treatment of arteriosclerosis and thrombosis. The treatment of stenotic and occlutic blood vessels depends in part on the severity of the blockage and the location thereof. In the case of coronary arteries, it is common to perform coronary bypass surgery to provide blood vessel shunts to restore blood flow past a severely blocked or occluded artery. This procedure is also utilized in other blockages in the peripheral vasculature.
As an alternative to surgery, balloon angioplasty has been utilized to expand accumulated deposits, or plaque. The method includes the insertion of an inflatable balloon, which is positioned at a stenosis and thereafter inflated to dilate stenotic arterial segments. This may obviate arterial bypass operations. However, balloon angioplasty has a number of limitations which include arterial dissection, bleeding, and reocclusion. In addition, re-stenosis is a common occurrence and near total blockages or occlusions are not treatable by balloon angioplasty techniques since the balloon cannot penetrate the occlusion.
Ultrasonic energy has been suggested for removal of intravascular blockages due to atherosclerotic plaque and intravascular blood clots. It has been shown that ultrasonic energy is useful in fragmenting plaque and thrombosis, either as a result of mechanical action thereon or cavitation thereof, in which high energy ultrasound applied to liquids generates vapor-filled microbubbles, or "cavities," with the concomitant rapid expansion and collapse of the cavities, accompanied by local intense hydraulic shock leading to fragmentation or dissolution of the thrombosis.
Heretofore developed equipment for the ultrasonic elimination of plaque and the like has included apparatus for the generation of the ultrasonic energy exterior to the body and the transmission of the ultrasonic energy into the body through a transmission wire to the stenosis site. Although good ultrasonic plaque ablation has been shown using an intravascular device consisting of a 2 mm titanium ball which is vibrationally excited by a 0.015 inch (0.38 mm) diameter titanium wire, these devices do not allow deployment in desired regions due to the stiffness of the transmission wire.
Unfortunately, when the wire diameter is reduced to lower the stiffness thereof, it can no longer deliver sufficient energy to the ball for surgical procedures.
The apparatus of the present invention eliminates the use of ultrasonic transmission wires by providing in situ generation of ultrasonic energy and direct ultrasonic radiation therefrom, which is capable of ablating plaque and dissolving clots even when the artery is totally occluded and which can be safely deployed in the arterial region of the heart itself.